During the past three years the following accomplishments have been made: Correlation of fatty acid composition of microsomal lipids modified by dietary means with enzyme activities of microsomes revealed no drastic differences, only minor trends. Isomeric octadecynoic acids and isomeric cis and trans octadecenoic acids were tested as possible inhibitors of desaturation and most were found to be inhibitory. cis delta 10- and delta 11 18:1 were most inhibitory. The products of pyrolysis of saturated triglycerides were separated and identified and found to contain heterocyclic products. Analyses of serum and adipose tissue lipids of cases of Prader-Willi obesity syndrome revealed unusually high proportions of PUFA in the triglycerides. The EFA deficiency induced by long term intravenous feeding of humans has been fully characterized. Chlorinated pesticides have been found to diminish the capability of liver microsomes of rats to desaturate and to elongate fatty acids. The proposal includes study of the effect of fatty acid structure upon the metabolism of the fatty acid. This will be studied via alteration of tissue lipid fatty acids by dietary means, and by study of the effects of an isomeric series of acetylenic acids, and of certain polyynoic acids upon metabolic reactions in vivo and in vitro. The prevention or treatment of the EFA deficiency induced in humans by prolonged intravenous alimentation will be studied intensively. The effects of various dose levels and durations of doses of intravenous fat emulsion will be documented. The effects of application of polyunsaturated oils to the skin upon the deficiency will also be studied.